To clearly illustrate the activity effect of multi-walled carbon nanotubes (MWCNTs) and their functionality on anodic exoelectrogen in microbial fuel cells (MFCs), the growth of E. coli and anode biofilm on MWCNT-, MWCNT-COOH and MWCNT-NH2-modified anodes were compared with a bare carbon cloth anode. The activity effect was characterized by the amount of colony-forming units (CPUs), activity biomass, morphology of biofilms and cyclic voltammetric (CV). The results showed that MWCNTs, MWCNT-COON and MWCNT-NH2 exhibited good biocompatibility on exoelectrogenic bacteria. The performance of MFCs were improved through the introduction of MWCNT-modified anodes, especially in the presence of -COOH/NH2 groups. The MFCs with the MWCNT-COOH-modified anode achieved a maximum power density of 560.40 mW/m(2), which was 49% higher than that obtained with pure carbon cloth. In conclusion, the positive effects of MWCNTs and their functionality were evaluated for promoting biofilm formation, biodegradation and electron transfer on anodes. Specifically, the MWCNT-COOH-modified anode demonstrated the largest application potential for the development of MFCs. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.